Suspension type heat exchanger for finely divided solids



Feb. 25, 1958 .'G,'N|EM|TZ 2,824,384

SUSPENSION TYPE HEAT EXCHANGER FOR FINELY DIVIDED SOLIDS Feb. 25, 1958 G. NIEMl'rz 2,824,334

` SUSPENSION TYPE HEAT EXCHANGER FOR EINELY DIVIDED soLIns Filed July 25. 1954 :s sheets-sheet 2 FIG. 2

Gos Duct Gos Duci Dust l Du st Collector Collector Emergency Gole lNVENTOiR Gerhard N'emllz ATTORNEYS G. NIEMITZ I Feb. 25, 1958 SUSPENSION HEAT EXCHANGER FOR FINELY DIVIDED SOLIDS 3 Sheet--Sheet 3 INVENTOR Gerhard Nie mitz a. me

y Filed July 23. 1954 2,824,384 Patented Fee. 25, 195s SUSPENSION TYPE HEAT EXCHANGER FOR FINELY DWHDED SLEDS Gerhard Niemitz, Bronx, N. Y., assigner to Kein-sedi'n Van Saun Mfg. e Eng. Corp., New York, N. Y., a corporation of Delaware Application July 23, 1954, Serial No. 445,305

10 Claims, (Cl. F14-56) This invention relates to improvements in heat exchangers for preheating finely divided solids. More particularly the invention relates to an apparatus for preheating the dust-like material constituting the dry charge for cement kilns, and a preheater or heat exchanger for carrying out the preheating.

Finely divided material of the type referred to above is preheated in contact with highly heated gases in known types of equipment which are unnecessarily expensive to construct and operate. For example, a particular preheater or heat exchanger of known construction requires a fan which gives a pressure of 28 inches of water and requires a power consumption of 190 H. P. Furthermore, in this known type of heat exchanger the radiation losses are excessive because of the use of large diameter piping and cyclone separators located in positions where they radiate large quantities of heat.

The drawbacks and disadvantages of this known type of heat exchanger are overcome by providing a heat exchange tower in which the intimate contact between the dust-like particles to be heated and the heating gas is effected during the parallel flow of these materials. It has been discovered that by utilizing the principle or" parallel flow heat exchange, it is possible to construct a heat exchange tower occupying not more than one-half the space of known constructions and in which the heating gases are handled at relatively low pressure differentials and with a relatively low power consumption, for example, the pressure differential is only 6.2 inches and the power requirement is 42 horse power, as compared to the figures given above.

In a preferred form of construction, the improved tower heat exchanger comprises a series of chambers provided with baffles over which the fine solid material drops in succession from an elevated feed bin, the finely divided material passing through a series of air locks or rotary valves downwardly through the tower to the point where it enters the inlet of a cement kiln, for example. In this construction the gas travels in parallel flow with the finely divided solid material through the series of chambers, at the bottom of each section of which the gas is forced to make a sharp 180 turn, so that most of the dust or solid material is separated therefrom. After leaving one chamber or section, the gas travels upward to the top of the next higher section of the series where its direction of flow is reversed and it again travels in parallel ow downwardly with the fine material being preheated, The intimate contact and separation of highly heated gas and finely divided solid is accomplished in each of the series of zones or sections. After the gas leaves the final heat transfer compartment or section, it is conducted through a cyclone type dust collector for the removal of any finely divided material which may have been carried by the gas stream. These cyclone separators discharge the dust through air locks into a mixing zone where it is mixed with dust previously separated from the gas stream in the first zone of the series, in the direction of solids flow. This mixing compensates for any segregation of solid parv cement kiln l@ of the rotary type.

ticles due to difference in sizing in the series of zones, since all material must pass through the same heat transfer sections or compartments.

in the preferred construction the preheated dust separated out in each zone or section is passed from that section through a rotary feed valve or air lock into a downwardly-fiowing gas stream of higher temperature in the next lower section of the series. Furthermore, the heat exchange tower is advantageously divided into similar parallel sections where parallel streams of hot gases respectively contact separate streams of downwardly flowing solid particles of material to be preheated. Invthis construction the two streams of gas are preferably mingled after one or more heat exchange contacts and then -divided again into streams for separate individual contacts.

The improved construction advantageously includes means for automatically operating the air locks or rotary feed valves to prevent clogging or injury to the equipment. rhesc rotary gates or air locks are protected by a grid againstthe entry of large pieces of har-d material which may accidentally drop from the contact shelves in the heat exchange Zones. These pieces of hard material may, for example, be pieces of re brick or pieces of condensed alkali or other materials being processed. Any smaller pieces which pass through the protecting grid and which may accidentally jam the leading edge of the rotary gate are automatically freed by reversal of the direction of rotation of the rotary gate or lock. This permits the freedpiece to drop into the bottom of the gate pocket so ythat it can be discharged to the next heat exchange zone or section.

The gates and mountings are preferably constructed of high temperature alloy metals and these structures are protected against excessive heat by forced air cooling, the air for cooling the rotary gate being directed through the center of the rotor. The gates are so constructed that very little gas leakage is encountered, but in any case, there is very little leakage because the draft differential between the succeeding heat exchange stages or sections is very low. This low differential permits of a very liberal clearance between the gate rotor and the housing thereof.

Electrically operated means is providedfor reversing the direction of rotation ofthe rotary gates or valves, as`

described more in detail hereinafter.

The improved apparatus of the present invention includes other features and details which are described hereinafter in connection with the accompanying drawings which illustrate one. embodiment of the invention.

ln the drawings:

Fig. l comprises a side elevational view of Aa heat exchange tower operatively associated with the feed end of a cement kiln and constructed in accordance with the features of the invention, with parts broken. away;

Fig. 2 is a vertical sectional view of the heat exchange tower taken at right angles through approximately the center of the tower shown in Fig. 1;

Fig. 3 is an enlarged broken vertical sectional View similar to that of Fig. 2 .showing the details of the rotary valve or gate construction; and

Fig. 4 is a diagrammatic view including a wiring diagram for the automatic operation of the feed valves or gates.

Referring to Figs. l and 2, the installation is illustrated in connection with the supply of finely divided or pulverized dust-like charging stock or raw material to a In Fig. l the .inlet end of the kiln i@ is shown directly connected to a feed chute ii vhaving an arcuate or curved slanting bottom. The feed chutey li leads into the lower portion of a heat exchange tower i2 having a steel-work supporting frame including columns 13. While the heat exchange tower has a steel-work frame, its walls and various structures forming the heat exchange compartments, passages and gas ducts are made of refractory material in accordance with well-known principles of construction where high temperatures are involved, of the order of those of the gases discharged from rotary cement kilns for making Portland cement.

The upper portion of the heat exchange tower 12 includes a feed bin 14 having a considerable capacity for holding the finely ground raw material for making Portland cement, such material being charged to the bin 14 through an opening 15 at the top, for example, by an air lift from raw material grinding mills. The bin 14 has a pair of sloping bottom portions which respectively terminate in discharge passages occupied by rotary feed valves 16 extending horizontally, transversely of the tower 12,

The tower 12 is generally rectangular in cross-section with its narrower' dimension shown in Fig. l, while its wider dimension is shown in Fig. 2. The horizontal feed valves, such as 16,` extend transversely with respect to the dimension shown in Fig. l, so that a wide hand of finely divided material is delivered by each feed valve at a pre` determined rate depending upon the rate of rotation of the valves.

The feed valves 16 discharge respectively into heat transfer chambers 17 and 18. In each of these chambers =or zones the dust-like material falls on and slides down the sloping surfaces of alternately arranged shelves or baffles `19 until it reaches the lower end of the zone or ychamber where it collects above rotary gates 20 and 21, respectively. These gates or feed valves function in the same manner as the valves 16 and `supply finely divided and partially preheated material to heat exchange chambers or zones 22 and 23, respectively, which are similar in construction to the zones 17 and 18.

At the bottom of the heatexchange chambers or compartments 22 and 23, the finely divided material normally accumulates above rotary valves 24 and 25, respectively, which supply preheated finely divided material to the final highest temperature preheating chambers or zones 26 and 27, respectively, in the lower portion of the tower 12. These latter chambers deliver the highly preheated raw material onto rotary valves or gates 28 and 29, respectively, which discharge into the chute 11 leading to the inlet of the kiln 10.

The finely ground raw material for making cement is heated by direct transfer from the high temperature gases produced from burning the raw material to Portland cement in the kiln 10. These gases at a very high temperature are discharged from the material inlet end of the kiln through the chute` 11 of relatively large cross-sectional area directly into a relatively large area rectangular shaped passageway 30, as shown in Fig. 2, extending transversely of the kiln between the heat exchange compartments or chambers 26 and 27. The passageway 30 is de fined by transverse walls 31 which are shown as terminating somewhat below the rotary feed valves 24 and 25 so that the high temperature gases from the passageway 3i) divide at the top of this passageway and flow over the walls 31 into the respective chambers 26 and 27 in direct contact with the fine powdered raw material discharged by the rotary valves 24 and 25. The raw material is, therefore, preheated while it is directly in suspension in the high temperature gases, the alternating baffles 19 causing the gases and suspended raw material to change their direction of tiow as they move downwardly together through the chambers 26 and 27.`

The walls 31 cooperate with opposite walls 32 to define the chambers 26 and 27, respectively, and the walls 32 cooperate with the respective side walls 33 to provide passageways 34 and 35, respectively at opposite sides of the tower for the flow of high temperature gases from the respective chambers 26 and 27.

As thehigh temperature gases in the chambers 26 and ature gases and pulverized raw material.

27 reach the lower ends of these chambers with their suspended highly heated raw material, the gases make an abrupt turn around the lower ends of the walls 32 and flow respectively upwardly through the gas passageways 34 and, 35 to the top of the walls 32 over which they overflow into and downwardly through the respective zones or chambers 22 and 23. It will be noted that the upper part of the walls 32 comprise the outside walls of the chambers 22 and 23.

The same type of heat exchange operation and functions occur in the chambers 22 and 23 as that described in connection with chambers 26 and 27. The gas streams reaching the lower parts of chambers 22 and 23 flow around transverse walls 36, forming a central passageway 37. The heating gases from the chambers 22 and 23 are mixed in passageway 37 and combined into one stream which divides into two streams which overflow the top of the walls 36 into the respective zones or chambers 17 and i8. The walls 36 not only define the passageway 37 but also, in the construction shown in Fig. 2, serve to define in part the chambers 17, 18, 22 and 23. Chambers 17 and 1S are bounded by outside walls 38 around the lower ends of which the gases flow respectively into passageways 39 and 49. The gas streams owing upwardly in the gas passageways 39 and 40 respectively flow out through openings 4l and 42 into dust collectors 43 and 44 from which the now relatively cool gases flow into a gas duct 45 connected to the intake of a fan, not shown, which delivers the gases into a stack 46 (Fig. 1) adjacent to the tower 12.

The heat exchange operation carried out in the tower 12 takes advantage of the parallel flow of high temper- This parallel flow takes place in each section of the heat exchange tower. At the bottom of each section the stream of gas is forced to make a sharp 180 turn so that most of the dust is separated from the gas stream. From this point the gas travels upwardly to the top of the next heat exchange section where it again travels in parallel flow with the material to be heated, The heat exchange sec tions and the general structure of the tower and its passages are of such a nature that the gas velocity is kept low so that the proportion of dust in the rising gas streams is relatively low. Any dust which is carried up with the gas stream in any instance is returned to the dust or fine raw material traveling downward in the next heat exchange chamber or zone. Any dust which is carried upward from one zone and downward through the next zone receives additional heat transfer.

The dust collectors 43 and 44 on opposite sides of the tower and respectively connected into the passageways 39 and 40, are standard cyclone type dust collectors so that their interior structures are not shown. The dust collected by these cyclones 43 and 44 passes through air locks or rotary valves 47 and connecting downwardly-inclined passageways 48 and 49, respectively, to a point above the respective air locks or rotary valves 21 and 20. The line dust, therefore, collected by the cyclones 43 and 44 is mixed with thel raw material dust passing downward through the tower so that any segregation which has taken place due to difference in sizing of the dust particles will be evened out again as all material must pass through the same or corresponding heat transfer chambers and eventually reach the rotary kiln 10.

Above the gas flow passageway 30, the tov er is provided with a deflecting wall structure including similar transverse wall sections 50 which are inverted V-shapcd in cross-section and respectively extend to the gates 24 and 25. An emergency gate or rotary valve 51 is mounted between the wall sections 50 for use in the event that either or both of the rotary valves 24 and 25 become stopped up or out of operation. lf this happens with either one of these rotary valves, the raw material will accumulate above the valve until it overflows the top of one of the walls 50 to the rotary valve 51 which showers the raw material downwardly through the passageway 30 where it is preheated in contact with rising gases and reaches the chute 11. Some part of thisV raw material delivered by the rotary` valve 51 may be carried by the gas stream into one of the chambers 26 .or 27 and, therefore, be delivered through gate 28 or 29. The rotary valve 51 continues the operation until valve 24 or 25 can be cleared.

Inspection and repair doors 52 are provided at least on one side of the tower directly above the position of each of the rotary gates soA that such gates may be inspected or repaired. Ifthe gate 20, for example, should become stopped up or otherwise'go out of operation, this would be noticed through the door 52 and the rotary gate 16 could be stopped temporarily so that there would not be `an accumulation of raw material above the gate 20 to any great extent. The rotary gate 47 would also be stopped until the gate 2t) was put back in operation.

In case of serious diiiiculty the flow of raw material to and the flow of gas through the tower may be discontinued for the purpose of making repairs, the hot gases at that time sent through a bypass 53 leading from the passageway 30. and delivering the hot gases directly into the stack 46. Normally, this passageway is closed by a heavy bypass damper 54. In order to facilitate inspection and repair of the rotary valves at various levels in the tower, the tower is provided with platforms 55 which also serve to support the motors and other equipment for operating the rotary valves; only one motor 56 and its control 57 are shown, for the rotary valve 28. Stairways not shown lead from the ground level successively to the different platforms of the tower.

Fig. 3 shows in enlarged detail a preferred type of construction for the rotary valves and the associated mountings therefor arranged in the refractory brick work of the tower. All of the rotary valves may be constructed alike as illustrated by the structure shown in Fig. 3 for the rotary valve 29. In this view the rotor, as shown, comprises a longitudinal body portion provided with an axial openingV 58 through which cooling air is forced by a fan or blower, not shown. The body includes a number of radially extending blades 59 defining intervening pockets for the reception of inely divided material to be transferred through the valve structure to the next lower section or to the chute 11 leading to the kiln.

The valve rotor, as shown in Fig. 3, is operatively associated witha metal mounting set in the refractory work of the tower and including hollow transversely extending spaced side sections 60 having arcuate portions fitting over the upper side portions of the rotor, and downwardly and inwardly sloping opposite upper surfaces along which lthe finely divided material flows to the rotor. The mounting structure also includes a grid or grating 61 covering the opening in the mounting and arranged to catch and exclude large particles from entry to the rotor. Cooling air from the blower referred to, and not shown, is forced through the hollow elements 60 of the mounting to prevent them from softening or melting. All of the metal elements of the rotary valve structure including the mounting are made of high temperature alloy. metals. When any large particles of material or pieces of tire brick are found on the gratings or grids 61lthey may be raked out through the adjacent door 52. The lrotors such as 29Aare provided with hollow end shaft sections whichlextendthrough the refractory side walls ofthe. tower and may be open to the atmosphere at one endand connectedto a blower at the other end.

The blower or blowers `may be located on one or more of the platforms 55.

Fig. 4y shows diagrammatically the arrangement for operating the rotary valves, such as 16, 20, 24, 28, 51 etc., this View showing a single unit for operating the motor 56 (Fig. l) for driving the rotary. valve 28, preferably througha clutch. and sprocket. The wiringl arrangement and relays shown in Fig. 4 may be housed and included in the control 57, having a double throw contacter arm 57 operated by a prong on a sprocket. The motor 56 is indicated diagrammatically in connection with its windings, and in association with relays 62 and 63 for connecting the motorto a three wire current supply 64 for respectively operating the motor in either direction of rotation. The motor 56, with the control shown, will continue to operate in the same direction so long as it does not become overloaded. When a piece of solid material catches between the edge ofv one of the blades 59 andthe mounting 60, the rotor will be stopped and the motor 56 will become overloaded, which will, for example, open an overload switch 65 and de-energize the relay 62, as shown, thereby cutting off the power for rotation of the motor in 'that direction. As the relay 62 is de-energized, it closes a switch 66, thereby permitting current to ow from one of the current supply lines 64 through a hand switch 67, the switch 66, an overload switch 68, and the coil of relay 63 through a switch 70 of a double throw switch unit 69, closed by the motor, to the neutral line of the power supply 64. When the relay 63 is energized, the current supply leads 64 are connected through the upper three switches of the relay to operate the motor S6 in the opposite direction to the one in which it was previously operated. This will permit any solid piece of material be tween a rotor blade and the mounting 6i) to fall into a cavity of the rotor and thereby be discharged through the rotary valve. The relay 63 also closes a switch 71 which applies a holding current on the relay 63, since the motor when reversed will open switch 7@ and close a switch 74.

Eventually the overload switch 65 closes, but since it is in seriesrwith a now open switch 72 of relay 63, it has no effect on the system. However, if the motor should now become overloaded because of the jamming of the rotary valve 28, for example, the overload switch 68 will open, the relay 63 will be de-energized and relay 62 en ergized. When the motor 56 was previously reversed, it shifted the double throw switch unit 69 to open switch 70 and close switch 74. As soon as the relay 62 is energized the motor is rotated in the opposite direction by current supplied through Athe upper three switches of the relay 62. As this relay closes the switch 66 is opened and a switch 75 is closed to provide a holding circuit on the relay 62 through switches 65 and 72. The switch unit 69 is shifted by an arm 57' which is rocked one way or the other by a spring prong 76 carried by a sprocket 77 mounted on the shaft of the rotary valve 2S andv driven by a drive chain from the motor 56.

While the foregoing system is sulicient in most instances for taking care of the reversal of rotation of the rotary valves of the heat exchange tower installation, modified forms of controls may be provided. For example, a switch may be provided directly in series with the hand switch 67 for interlocking the control with other motors. The overload switches 65 and 68, are shown diagrammatically responsive to overloads in the respective pairs of power supply lines to the motor. These overload switches are conventional.

It is to be understood that switches 76 and '74 may be shifted by any means actuated by the slowly rotating sprocket 77, operated by the motor 56, so that the double throw switch unit 69 is shifted in a direction for later reversing the direction of rotation of the motor. If the motor is stopped by openingthe manual switch 67, when under control of relay 63, the double throw switch unit 69 is in position closing the switch 74, ready to start the motor operating in the direction controlled bythe relay 62.

If the particles supplied to or condensed in the heat exchange operation are suliiciently large, it is possible that the motor or motorsmay reverse a number of times during a'days operation.

It is to be understood that a control system such asl that shown in Fig. 4 or equivalent thereto is provided for the motors or other driving or power means for all of the rotary valves with the possible exception of the rotary valves 47 which normally would handle nothing more than dust and which would not be likely to encounter any pieces of fire brick since the dust collectors are preferably of sheet metal construction.

The suspension type heat exchanger and method of heating finely divided solids as described above in connection with the drawings provides an installation and method which is very eflicient for utilizing the heat content of high temperature gases and for heating finely divided solids, or the reverse. Furthermore, the parallel or concurrent intimate contact flow of heating gas and finely divided solid to be heated is a very effective method for prolonging'the contact without the use of equipment large in dimensions as has been used in the past with `countercurrent flow. Furthermore, the draft loss throughv the installation of the present invention is extremely low,

`amounting to approximately 6 inches of water as against 28 inches for other known types of preheaters. This Yamounts to a saving in power of` approximately 78%, vor for a 300 ton per day plant, a power consumption of `only 42 horsepower for the exhaust fan, instead of 190 horsepower in other known types of preheaters.

In the installation according to the present invention,

the total radiation loss is only a fraction of the loss experienced with other preheaters because the total exposed radiating surface is relatively small on account of the compact arrangement of the heat exchange chambers or zones made of fire brick and insulation in a steel shell. This means that the raw material can be heated to a higher temperature with a corresponding saving in overall fuel consumption.

The installation of the present invention, because of its compact construction occupies a total ground or oor space of only about one-half of that required in a preheater in which cyclones are used as the heat exchange zones. Furthermore, the total cost of the installation according to the invention is extremely low compared to known installations of equal capacity, since no separate building is required for the tower preheater. With the exception of the steel housing, columns, stairways, platforms, dust collectors, feed bin and rotary gates, the whole construction is of refractory and insulating materials.

The specific details of the circuit arrangements of the electric motor for operating the rotary valve type distributor are claimed in the applicants divisional application Ser. No. 568,592, filed February 29, 1956 for Rotary Feed and Distributor Valves and Operating Mechanism Therefor.

What I claim is:

l. A heat exchange installation for exchanging heat between a liuid gaseous medium and a finely divided solid material, comprising a series of heat exchange chambers, means for passing the finely divided solid material in succession through said series of chambers from one end of the series to the other, the series of chambers being arranged one below the other in the direction of passage of the `finely-divided solid material through the series of.chambers, means for distributing the finely-divided solid material into the upper portion of each chamber, means for passing the fluid gaseous medium in succession through the series of chambers in the reverse order to that of the passage of finely divided solid material, means for causing the finely divided solid material and fluid gaseous medium to flow downwardly through each chamber of the series in concurrent intimate contact with each other, means for causing the separation of finely divided solid material from the fluid gaseous medium following their concurrent flow and intimate contact in each chamber, and means for conducting the resulting separated fluid gaseous medium into the upper portion of the preceding chamber of the series relative to the direction of passage of the finely-divided solid material through the series of chambers.

2. An installation as claimed in claim l, in which the means for passing the iiuid gaseous medium includes means for causing the flow of said medium from the lower portion of each chamber to the upper portion of the next higher chamber, said distributing means being adapted to exclude the flow of the gaseous medium.

3. An installation as claimed in claim 2, in which said distributing means comprises a rotary valve for feeding finely divided material, means for rotating said valve, and means responsive to the stoppage of Said valve for reversing its direction of rotation.

4. An installation as claimed in claim 3, in which the means for rotating the rotary valve includes an electric motor, and in which the means responsive to the stoppage of the rotary valve includes an overload relay, and means responsive to the operation of the overload relay for reversing the electric motor.

5. A heat exchange tower installation for exchanging heat between a uid gaseous medium and a finely divided solid material, comprising a tower structure divided into a series of heat exchange chambers arranged one above the other in the tower, means for feeding finely divided material into the upper portion of the uppermost chamber in the tower, means for feeding finely divided material from each chamber except the lowermost into the upper portion of the next lower chamber, means for conducting the uid gaseous medium in a stream upwardly through the tower including a passageway for introducing the fluid gaseous medium into the upper `part of the lowermost chamber for ow downwardly therethrough concurrently with the finely divided solid material fed thereinto, and a passageway for conducting fluid gaseous medium from the lower portion of each chamber into the upper portion of the next higher chamber of the series for concurrent flow downwardly therethrough `with the finely divided solid material fed into said next higher chamber of the series.

6. An installation as claimed in claim 5, in which the lower portion of each chamber includes a structure causing the gaseous medium to make a change in the directoin of flow, whereby finely divided solid material carried by the gaseous medium through the chamber is caused to separate from the gaseous medium.

7. A heat exchange installation as claimed in claim 1, in which the chambers are arranged in vertical series and in which each chamber includes a series of alternately arranged batiles adapted to cause the material and medium to take a zigzag course downwardly through the chamber.

8. A heat exchange tower installation for exchanging heat between a fluid gaseous medium and a finely divided solid material, comprising a tower structure including at least two series of heat exchange chambers the chambers of each of which are arranged one above the other in the tower, said two series of chambers being spaced apart laterally to provide intermediate passageways for liuid gaseous medium, one of said passageways being arranged between the spaced lowermost chambers and opening into the upper portion of each of said lowermost chambers, a dividing wall structure arranged directly above said lowermost chambers, means for feeding finely divided material into the upper portion of the uppermost chambers of both series in the tower, means for feeding finely divided material from each chamber of both series except the lowermost into the upper portion of the next lower chamber, such means for said lowermost chambers comprising a rotary distributor in said wall structure for each chamber, a rotary distributor intermediate said distributors for distributing finely divided solid material into said one passageway in the event one of the other distributors becomes inoperative, means for conducting the fiuid gaseous medi um in a stream upwardly through the tower including said one passageway for introducing the fluid gaseous medium into the upper portions of said lowermost chambers for ow downwardly therethrough concurrently with the finely divided solid material fed thereinto respectively by said distributors, and a passageway for conducting uid gaseous medium from the lower portion of each chamber of each series into the upper portion of the next higher chamber of the same series for concurrent ow downwardly therethrough with the finely divided solid material fed into said next higher chamber.

9. In an apparatus for preheating finely divided solid raw material to be used in the manufacture of Portland cement, a tower divided into a series of heating chambers of high temperature refractory material adapted to withstand the high temperatures of Portland cement kiln gases, said heating chambers being arranged one above the other in the tower, means for feeding and distributing the nely divided raw material to be preheated into the upper portion of the uppermost chamber in the tower, means for feeding and distributing the raw material reaching the lower portion of each chamber, except the lowermost, directly into the upper portion of the next lower chamber of the series, a gas ow passageway of high temperature refractory material for conducting high temperature cement kiln gases into the upper portion of the lowermost heating chamber to ow downwardly therethrough concurrently with the nely divided raw material distributed thereinto, and a gas ow passageway of high temperature refractory material for conducting heating gases from the lower portion of each heating chamber, except the uppermost, into the upper portion of the next higher heating chamber of the series to ow downwardly therethrough concurrently with the finely divided raw material distributed thereinto.

l0. An apparatus as claimed in claim 9, in which each gas flow passageway and the heating chamber into which it is connected have a common wall of high temperature refractory material.

References Cited in the le of this patent UNITED STATES PATENTS 1,863,803 Pantenburg June 21, 1932 2,187,799 Baughman Jan. 23, 1940 2,361,151 Reed Oct. 24, 1944 2,395,090 Arnold Feb. 19, 1946 2,428,241 Pootjes Sept. 30, 1947 2,530,181 Schilling Nov. 14, 1950 2,548,262 Hintz Apr. l0, 1951 2,648,532 Muller et al Aug. ll, 1953 2,663,465 Hogin Dec. 22, 1953 2,757,921 Petersen Aug. 7, 1956 2,766,534 Schaub et al Oct. 16, 1956 FOREIGN PATENTS 212,671 Great Britain Mar. 20, 1924 

